Touch screens have become common in modern mobile phone user interfaces. A touch screen typically comprises a surface with a matrix of touch sensitive nodes and a processor connected to scan through the matrix to detect the state of each node. There are various types of touch screens, such as resistive, capacitive, optical and pressure sensitive touch screens. The physical operation of the nodes depends on the type of the touch screen, but in common the nodes electrically indicate touch of a finger or stylus to the processor at the node in question and the processor deduces from the states of the nodes the area or areas being touched in a particular detection frame. The detected areas of a detection frame are provided by the processor to a host device for processing as user input.